### Locating the Epicenter

```Start here
• S-Waves
• These waves
vibrate in a
side to side
motion
Surface
• P-Waves
• These waves
move in a
compress and
expand motion
• They are the
first to arrive to
the epicenter
Secondary
Primary
There are three seismic waves
• L-Waves
• These waves
move in an up
and down
circular motion
• Most
destructive
wave
Continue to Seismogram
Back to Seismic Waves
Back to Seismic Waves
•The picture with the squiggly line is called a seismogram
•It measures how big the seismic waves are
•The seismogram is a piece of paper located on seismograph
•A seismograph measures the intensity of the earthquake at a certain
location
•It does this by having a weight hold a pen as the earth shakes, the
pencil stays still as a squiggly line is created
•The more shaking the bigger the lines
•The picture to the right is a seismograph
Let’s see how we use this
This is when the S-wave arrives
This is
when the
P-wave
arrives
The difference in time between when the P-wave arrives and
when the S-waves arrives, also know as lag time. This is
important because it will tell you how far away you are from
the epicenter.




A. Locate the how long the P-Wave shakes the
seismogram.
B. Find when the S-wave arrives, then the Pwave, and find the lag time between the two.
C. Find when the P-wave arrives, then the Swave, and find the lag time between the two.
D. HELP!!
This is when the S-wave arrives
This is
when the
P-wave
arrives
The difference in time between when the P-wave arrives and
when the S-waves arrives, also know as lag time. This is
important because it will tell you how far away you are from
the epicenter.
This is when the S-wave arrives
This is
when the
P-wave
arrives
The difference in time between when the P-wave arrives and
when the S-waves arrives, also know as lag time. This is
important because it will tell you how far away you are from
the epicenter.
City
P-wave Arrival
Time
S-wave Arrival
Time
Lag Time
Washington DC
2:10
2:11
1 minute
New York
2:14
2:17
3 minutes
Chicago
2:19
2:24
5 minutes
B.
City
P-wave Arrival
Time
S-wave Arrival
Time
Lag Time
Washington DC
2:10
2:11
1 hour
New York
2:14
2:17
3 minutes
Chicago
2:19
2:24
4 minutes
City
P-wave Arrival
Time
S-wave Arrival
Time
Lag Time
Washington DC
2:10
2:11
1 minute
New York
2:14
2:17
3 minutes
Chicago
2:19
2:24
5 minutes
This is one
should be 1
Minute
City
P-wave Arrival
Time
S-wave Arrival
Time
Lag Time
Washington DC
2:10
2:11
1 hour
New York
2:14
2:17
3 minutes
Chicago
2:19
2:24
4 minutes
This one should be 5 minutes
Let’s
move on
I do not
understand .
1st Step – Figure out the size of
the lag time. Let’s use 1 minute
as an example.
2nd Step – Find where the Pwave and S- Wave have the
measurement of the lag time.
3rd Step - find the distance below.
1. This is how
big one minute
is
2.This
is
where
the lag
time is
one
minute
3. Your
distance is
about 300
miles
This graph is available at bryonspicci.sslpowered.com
Let’s
move
on
I do not
understand .
1st Step – Figure out the size of
the lag time. Let’s use 1 minute
as an example.
2nd Step – Find where the Pwave and S- Wave have the
measurement of the lag time.
3rd Step - find the distance below.
1. This is how
big one minute
is
2.This
is
where
the lag
time is
one
minute
3. Your
distance is
about 300
miles
This graph is available at bryonspicci.sslpowered.com
Let say that at your location the
P-wave arrives at 9:30 and the
S-waves arrives 9:33, how far
are you away from the
epicenter?
A. 9000
B. 1200
C. 1000
D. 900
This graph is available at bryonspicci.sslpowered.com
Let say that at your location the
P-wave arrives at 9:30 and the
S-waves arrives 9:33, how far
are you away from the
epicenter?
A. 9000
B. 1200
C. 1000
D. 900
This graph is available at bryonspicci.sslpowered.com
Let say that at your location the
P-wave arrives at 9:30 and the
S-waves arrives 9:33, how far
are you away from the
epicenter?
A. 9000
B. 1200
C. 1000
D. 900
This graph is available at bryonspicci.sslpowered.com
Let say that at your location the
P-wave arrives at 9:30 and the
S-waves arrives 9:33, how far
are you away from the
epicenter?
A. 9000
B. 1200
C. 1000
D. 900
This graph is available at bryonspicci.sslpowered.com
Chicago
New York
Washington, DC
Washington, DC is 900 miles away
click on it
New York is 1200 miles away
click on it
Chicago is 1900 miles away
Click on it
Click here
to take the
quiz.
Chicago
New York
Washington, DC
I think I need
This is epicenter!
more help
before taking
the quiz
Write the answer in the box to the right.
1.
When locating the epicenter, the first thing someone must do is…
A. Draw three circles
B. Find the arrival time of the p-wave and s-wave
C. Find the lag time
D. Locate the focus
2.
When locating the epicenter, the second thing someone must do is…
A. Draw three circles
B. Find the arrival time of the p-wave and s-wave
C. Find the lag time
D. Locate the focus
3.
Lag time is the difference in time between the _________ and ___________.
A. Seismic wave and tsunami
B. P wave and T wave
C. Shake and Aftermath
D. P wave and S wave
After you find the distance a location is from the epicenter, you need to…
A. Draw a circle and find the possible locations
B. Draw a square and find the possible locations
C. Call it a day
D. Decide how big of a circle you need to draw around the epicenter
What is the minimum amount of locations you need to locate an epicenter?
4.
5.
Click here when all questions have been answered
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